Electronic heating apparatus and method



Feb 2, 1950 T. H. STORY ELECTRONIC HEATING APPARATUS AND METHOD Filed OGE.. 5l, 1945 INVENTQR ATTORNEY Patented` Feb. 21, 11950 ELECTRONIC HEATING APPARATUS AND METHOD Theodore H. Story, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 31, 1945, Serial No. 625,915

(Cl. 21S-47) 4 Claims. 1

This invention relates to an improved electronic heating apparatus and method, and more particularly to a method of and apparatus for locally heating dielectric articles electronically.

In many applications, it is desirable to heat dielectric articles rapidly in only a localized zone or region to a prescribed temperature without raising the surrounding regions to that temperature. For example, in putting up various food products for sale in containers of thermosetting or thermoplastic material, it is desired to seal the cover to the main body of the container without impairing the quality of the contents. The cover and body of the container need be heated only at the meeting surfaces thereof, but frequently to a temperature above that to which the food contents can be safely heated. Again, in the manufacture of phosphorous bombs which are encased in a Bakelite or other similar dielectric casing, the cover must be sealed to the body of the container in which the phosphorous is housed, and the sealing must be effected at a temperature above the melting temperature of the phosphorous. In all such applications, it is essential that the contents be maintained at a low enough temperature to prevent harmful effects thereon.

The primary object of my present invention is to provide an improved method of and apparatus for locally heating prescribed regions of dielectric articles with the aid of a high frequency electric eld in a manner such that no harmful effects are produced in other regions thereof.

More particularly, it is an object of my present invention to provide an improved method of and apparatus for raising the temperature of a localized region of a dielectric article, such as a hollow container made of either thermoplastic or thermosetting material, with suflicient rapidity to render plastic the thermoplastic material or to polymerize the thermosetting material at said region, as the case may be, or to accomplish any other desired heating effect, without overheating adjoining portions.

Another object of my present invemion is to provide an improved method of and apparatus for locally heating dielectric materials as aforesaid, which method and apparatus readily lend themselves to conveyor line operation.

Still another object of my present invention is to provide an improved method and apparatus as above set forth in which suitable temperature gradients will be set up between the locally heated portion of the work and the unheated portion thereof to avoid setting up undue strains and stresses therein.

It is also an object of my present invention to provide an improved method and apparatus as aforesaid which are economical in cost and highly eicient in use.

In accordance with my present invention, I apply to one side of the work around the region thereof which is to be heated locally a pair of electrodes of suitable shape or contour and connect these electrodes to a source of radio frequency or other suitable high frequency current. There is thus set up between the two electrodes a high frequency electric field having a stray component which links the region to be heated. This stray component of the electric field, which is normally highly concentrated, -rapidly raises to the desired temperature the region to be heated as a result of the dielectric losses which it produces therein. In many instances, however, the heat developed in this region is suflicient to bring the adjoining zones and, in the case of hollow containers, the contents thereof, to a temperature which may be harmful. In accordance with my invention, I provide the electrodes with suitable extensions which are also applied to the article in snug relation therewith, these extensions being arranged to extend away from each of the appended electrodes in a direction opposite to that of the other electrode in relation to itself. The electrode extensions are preferably made of material which is highly heat conductive as well as being electroconductive, and they keep the areas of the article to which they are applied cool first, by spreading the stray electric field or flux lines between the electrodes over a wide area, thereby reducing the flux density and the heating effect in the regions of the article beyond that to be heated, and secondly, by conducting away from the article over the areas to which they are applied the heat acquired by the article at said areas. The latter effect can be augmented by the use of a coolant. In any case, it is apparent that the heat is localized almost entirely in the region to be heated and the danger of overheating the adjoining regions or the contents, in the case of a container, is avoided.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will better be understood from the following description, when read in connection with the accompanying drawing in which Figure 1 is a transverse sectional view of one form of electronic heating apparatus according to my present invention, the apparatus being shown applied to a hollow, cylindrical container,

encaisse Figure 2 is a fragmentary sectional view illustrating the manner in which the high frequency electric eld which is set up between the electrodes is distributed when the electrodes are not provided with extensions in accordance with my present invention,

Figure 3 is a view similar to Figure 2 but showing the greater distribution of the field when the electrodes are provided with extensions according to my present invention. and

Figure 4 is a diagrammatic, plan View illustrating the manner in which my present invention may be utilized in a continuous, conveyor line operation.

Referring more particularly to the drawing, there is shown, in Figure 1, a cylindrical housing comprising a casing portion I which is open at the upper end and is threaded for the reception of a cover portion 3. rIhe housing I, 3 may be made of Bakelite or other suitable dielectric material and may be used for packing fruit, vegetables or other food products for the market, or it may be used as the housing for white phosphorous in a bomb, or the like. In any event, it may be assumed that the cover 3 is to be applied to the casing I and bonded thereto to seal the contents. For this purpose, the threads on the casing part I and the cover part 3 in the region A may be coated with a thermosetting cement which must be heated to a prescribed temperature at which it will polymerize. If this temperature is higher than that to which the contents of the housing can be safely subjected without suffering a deleterious effect, it is apparent that the heat must be localized in the region A or at the threads of the casing I and the cover 3.

To accomplish the desired heating, there is provided around the region of the threads, on each side thereof, a pair of ring-like electroconductive electrodes 5 and 'I which are connected to a source 9 of high frequency power, such as a vacuum tube oscillation generator operating at radio or other suitable high frequency. Since the electrodes 5 and 'I are both on the same side of the work (that is, the outside of the housing I, 3 in the illustrated embodiment), reliance must be had on the stray component S of the high frequency electric field which is set up between the electrodes 5 and 1, as distinct from the direct component D, to heat the region A where the heat is to be fairly localized. Now, it will be seen from Figure 2 that the stray field S is hunched and quite dense when the ring-like electrodes, which have a very small cross-sectional area, are employed by themselves. Such a field produces rapid heating to an elevated temperature in many instances suiicient to endanger the contents of the housing I, 3. To avoid this, I provide the electrodes 5 and 'I with extensions 5a. and la, respectively, these extensions being, in the illustrated embodiment, cylindrical members which may be formed integrally with the electrodes 5 and l, if desired. The extensions 5a and la are made of highly heat conductive material and are arranged to snugly t against the casing part I and the cover part 3. By providing the extensions 5c and 'Ia on the electrodes 5 and 1, respectively, the stray field S is caused to distribute itself over a greater area, as will be seen from Figure 3, thereby becoming less dense. As a consequence, the stray field will not heat the regions beyond the local region A where the heat is to be concentrated to as high a temperature as would the stray field component of Figure 2. In addition, the extensions or sleeves y 5a and 'Ia assist greatly in conducting away from the areas of the casing part I and the cover part 3 to which they are applied the heat acquired thereby. This eect may be enhanced by applying a stream of cooling air, water, or other coolant to the electrode structures 5, 5a and Ia, or they may be provided with cooling coils around them in known manner. In any case, this arrangement permits rapid heating of the threaded region of the housing I, 3 to the desired temperature without endangering the adjoining regions or the contents of the housing. Moreover, an electrode structure as above described will produce a temperature gradient between the heated and unheated regions which will be quite uniform and will therefore greatly avoid the danger of setting up undue strains and stresses in the wall structure of the housing.

An arrangement of electrodes with extensions as above described readily lends itself to conveyor line operation, as illustrated in Figure 4. In this figure, there is shown a fragment of a conveyor belt II which carries the articles I, 3 or other articles of dielectric material, `whether thermoplastic or thermosetting, past an operating station where brushes I5 and Il are located, the brushes I5 and Il being connected to the high frequency power source 9. The brushes I5 and II are so located that the brush I5 cooperates with the electrode extension 5a and the brush II cooperates with the electrode extension la, these brushes being engaged by the work as the various, successive articles constituting the work are advanced by the belt II. The brushes I5 and Il are made of a suitable length such that the time for which power is applied will be that necessary to heat the local region to produce the desired eiect.

I claim as my invention:

l. In electronic heating apparatus for localized heating of a dielectric article, a pair of spaced opposed heat conductive electrodes both adapted to be applied to one surface of said article'in heat conductive engagement therewith and to have set up therebetween a high frequency electric field having a stray component for linking said article and heating the region thereof between said electrodes, said electrodes being elongated and extending in opposite directions with respect to said i'leld to lie along said surface of the article in heat conductive contact therewith whereby the stray field component is reduced in density and the heating effect thereof is controlled within desired limits.

2. Electronic heating apparatus according to claim 1 characterized in that said elongated electrodes are constituted by relatively highly heat conductive material, and characterized further in that said electrodes are also shaped to fit said article in snug relation therewith to assist materially in conducting away from the areas of said articles to which they are applied the heat acquired by said article at said areas.

3. High frequency electronic heating apparatus, comprising in combination, a pair of electric current and heat conducting electrodes adapted to engage a surface of a dielectric article to be heated in heat conductive relation thereto whereby heat generated in said article is conveyed therefrom through said electrodes and dissipated by radiation therefrom, said electrodes being adapted to be positioned in close spaced end to end relation to each other on said surface of the material and being elongated to extend in opposite directions along said surface whereby a stray component of the high frequency eld between said electrodes is reduced in density.

4. The method of locally heating a prescribed region of a dielectric article with the aid of a pair of electrodes which comprises applying both said electrodes to one side of said article about said region, setting up between said electrodes a high frequency electric field having a stray cornponent which links said region and heats said region as a result of dielectric losses which it produces therein, causing said stray field component to be spread out beyond said region whereby to reduce the density thereof beyond said region to thereby minimize the heating effect thereof beyond said region, and further conducting heat from said material through said electrodes by 10 Number heat conductive contact therewith and radiation from said electrodes. THEODGRE H. STORY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

